A cathode ray tube (CRT) has been widely used as a display device. Recently, however, a flat panel display device, such as a plasma display panel (PDP) device, a liquid crystal display (LCD) device and an OELD, is used as a display device instead of the CRT.
Among these flat panel display devices, the OELD has an advantage in thickness and weight because the OELD does not require a backlight unit. The OELD device is a self-emission type display device. In addition, with comparison to the LCD device, the OELD has many advantages, such as a wide viewing angle, contrast ratio, low power consumption, and past response time. Moreover, since a fabricating method for the OELD is simple, there is another advantage of reducing production costs.
The OELD is classified into a passive matrix type and an active matrix type. In the active matrix type OELD, a thin film transistor (TFT) as a switching element is disposed at each pixel. Since the active matrix type OELD device has excellent capabilities of high resolution, low power consumption and lifetime with comparison to the passive matrix type OELD, the active matrix type OELD is much widely introduced.
FIG. 1 is a circuit diagram showing a pixel region of an OELD according to a related art. As shown in FIG. 1, a gate line “GL”, a data line “DL”, a power supply line “PL”, a switching thin film transistor (TFT) “STr”, a storage capacitor “StgC”, a driving TFT “DTr”, and an organic electroluminescent diode “E” are formed in one pixel region “P.” The gate line “GL” and the data line “DL” cross each other such that the pixel region “P” is defined, and the power supply line “PL” is formed to be parallel to the data line “DL.” The switching TFT “STr” is formed at crossing portion of the gate and data line “GL” and “DL.” The driving TFT “DTr” is electrically connected to the switching TFT “STr.”
The driving TFT “DTr” is electrically connected to the organic electroluminescent diode “E.” In more detail, a first electrode of the organic electroluminescent diode “E” is connected to a drain electrode of the driving TFT “DTr,” and a second electrode of the organic electroluminescent diode “E” is connected to the power supply line “PL” (not shown in the figure). The power supply line “PL” provides a source voltage to the organic electroluminescent diode “E.” The storage capacitor “Cst” is disposed between gate and source electrodes of the driving TFT “DTr” (not shown in the figure).
When a signal is applied to the switching TFT “STr” through the gate line “GL” such that the switching TFT “STr” is turned on, a signal from the data line “DL” is applied to the gate electrode of the driving TFT “DTr,” turning on the driving TFT “DTr.”. As a result, light is emitted from the organic electroluminescent diode “E.” Further, when the driving TFT “DTr” is turned on, a level of an electric current applied from the power supply line “PL” to the organic electroluminescent diode “E” is determined such that the organic electroluminescent diode “E” can produce a gray scale. The storage capacitor “StgC” serves as maintaining the voltage of the gate electrode of the driving TFT “DTr” when the switching TFT “STr” is turned off. Accordingly, even if the switching TFT “STr” is turned off, a level of an electric current applied from the power supply line “PL” to the organic electroluminescent diode “E” is maintained to next frame.
FIG. 2 is a schematic cross-sectional view of an OELD according to a related art. As shown in FIG. 2, the OELD 10 includes a first substrate 1 and a second substrate 2. The first and second substrates 1 and 2 are spaced apart from each other and attached by a seal pattern 20.
On the first substrate 1, a switching thin film transistor (not shown in the figure), a driving TFT “DTr,” a first electrode 3, an organic luminescent layer 5 and a second electrode 7 are formed. An absorbing element 13 for absorbing moisture is formed above the second electrode.
The driving TFT “DTr” is connected to the switching TFT (not shown in the figure), and the first electrode 3 is connected to the driving TFT “DTr.” The organic luminescent layer 5 is disposed on the first electrode 3, and the second electrode 7 is disposed on the organic luminescent layer 5. The first and second electrodes 3 and 7, and the organic luminescent layer 5 interposed between the electrodes constitute an organic electroluminescent diode.
The organic luminescent layer 5 provides red, green and blue colors. Specifically, first to third organic luminescent patterns 5a, 5b and 5c, which respectively emit red, green and blue color lights, are formed in each pixel region.
When the first electrode 3 is transparent and the second electrode 7 is opaque, light from the organic luminescent layer 5 passes through the first electrode 3 and the first substrate 1, but not much through the second electrode 7. This is referred to as a bottom emission type OELD. On the other hand, when the first electrode 3 is opaque and the second electrode 7 is transparent, light from the organic luminescent layer 5 passes through the second electrode 7 and the second substrate 2, but not much through the first electrode 3. This is referred to as a top emission type OELD.
Unfortunately, however, defects are generated in parts of a plurality of pixel regions. For example, some pixels constantly emit light because of an electrical shortage problem in electrical lines resulting from a static electricity or particles. This is referred to as a brightening point defect.